XRD Data Analysis Via Rietveld Refinement and Bandgap Studies of PbTi0.95Zr0.05O3 Perovskite

 

XRD Data Analysis Via Rietveld Refinement and Bandgap Studies of PbTi0.95Zr0.05O3 Perovskite

Kapil Vaishnave

Research Scholar at Department of Physics SAGE University

Indore (M.P.), India

Rajesh Kumar Katare

Professor at Department of Physics SAGE University

Indore (M.P.), India

AbstractZr modified PbTiO3, Pb(ZrxTi1x)O3 (PZT) has been under extensive research during the last decades as it inherits considerable ferroelectric, piezoelectric and other electrical properties. In this piece of work, we report 5% Zr doped PbTiO3 synthesized by solid state reaction route. The sample is nearly a single phased solid solution. The sample has been investigated for structural, optical bandgap and ac conductivity behaviour. The XRD data studies revealed tetragonal phase formation by the sample. The optical bandgap estimated from the Taucs plot reveals a bandgap value of 3.1eV. Since the sample displays nearly the insulating bahaviour, its frequency dependent ac conductivity is relatively low

KeywordsLead Zirconium Titanate, Solid State Route, Crystal structure, Optical Bandgap, ac conductivity

1. INTRODUCTION

   PbTi0.95Zr0.05O3 (PZT)is the most common ferroelectric (FE) material widely used in solid-state technology. It displays a strong piezoelectric property in polycrystalline form. The ferroelectric and properties along with better dielectric nature and wide band gap properties makes it favorable material to be used in transducers, ferroelectric FETs, sensors, actuators and non-volatile random-access memories [1-4]. Lead Titanate Zirconate (PbZr1-xTixO3) solid solutions known as PZT crystallize to the various distorted perovskite structures. These materials have drawn considerable interest for material researchers due to its interesting ferroelectric, piezoelectric and other electrical properties. Such materials are often used in ultrasonic generators, hydrophones, electronic buzzers and ringers, pressure and stress sensors, etc. Since their discovery in the early 50’s, PbZr1-xTixO3, or PZT ceramics are recognized as excellent piezoelectric materials [5,6]. At room temperature, the solid solution between lead titanate, PbTiO PbZr1-xTixO3 PbZr1-xTixO3 (PT), and lead zirconate, PbZrO PbZr1-xTixO3 (PZ), presents two ferroelectric phases, a tetragonal phase in the titanium rich side of the pseudobinary system, and a rhombohedral one in the zirconium rich side. This transition is usually classified as morphotropic because it corresponds to a structural change with the variation in composition [7,8]. In the thin films, PZT finds use in microelectro-mechanical-systems (MEMS), e.g., allows for the low voltage actuation as advantageous for gyroscopes, ultrasonic transducers or RF switches [9-11].

   It is well known fact that all the physical and chemical properties of the sample depends on particle size, morphology,

   crystal structure and the processing conditions. Therefore, method of preparation is expected to influence the properties of the sample. Scientists have developed various synthesis techniques which include solid state route, sol-gel method, RF sputtering, Pulsed laser deposition and various others. Among these methods, solid state route ensures better sample formation, with higher possibility of the single phase-ness. It however requires high temperature treatment which may induce structural inhomogeneities [11-14].

   In this project, we synthesized PbTi0.95Zr0.05O3material by solid state route. The synthesized sample is characterized for structural, optical and conductivities properties. XRD technique was exploited for structural determination, DRS UV-Vis spectroscopy was employed for optical bandgap determination, and for conductivity studies, dielectric measurement was carried.

2. PREPARATIONS AND CHARACERIZATIONS

   Synthesis

   To synthesize PbTi0.95Zr0.05O3material by solid state route, the precursors were PbO, TiO2 and ZrO2. All these oxide materials were used without pre-heating. The stoichiometric ratios calculated using on the molecular formula and weighed by a sensitive digital balance. The materials were mixed in the fixed ratio and were mechanically mixed using agate mortar and pestle for about 5h. The fine powder so obtained was calcined for 5h at 1000 oC. The same process was repeated once more. This is why the employed method is known as double calcination process. Duering grinding, acetone was used for proper dispersion of the precursors. The final powder was transformed into the pellets of the diameter of 10mm with 1mm thickness. The pellet was sintered at 1200 oC for 6h. The compact pellets so obtained was polished by silver oxide paste to form electrodes. This is done to carry out the dielectric measurements. Some powder form of the sample is retained for X-ray diffraction and optical bandgap measurements.

   Characterizations

   The sample was examined for structural studies using the most reliable X-ray diffraction technique in the angular range of 20o

   2 80o. The XRD data was recorded by using a PROTO AXRD Benchtop Diffractometer with Cu-K1 radiation ( = 1.5406Ã…). The sample was subjected to optical bandgap studies using UV-Vis Diffuse Reflectance Spectroscopy (DRS). To

   analyze the dielectric properties, Keysight Technologies’ Model E4980A Precision LCR meter was used. Here in this study, the dielectric data was converted by specific formula in to the ac conductivity of the sample. It is worth to mention here that all the characterizations were carries out at room temperature.

3. RESULTS AND DISCUSSIONS

   XRD Data Analysis

   For PbTi0.95Zr0.05O3known as Zr doped Lead titanate, we investigated the crystal structure and parameters related to crystal structure using X-Ray diffraction (XRD) characterization. The study of the XRD patterns witness the acquisition of tetragonal structure with space group P4mm [15,16]. The structure and other related parameters were determined using Rietveld refinement employing FullProf software. The Rietveld refined XRD data of the as prepared sample is displayed as Figure1. Some diffraction peaks skip the Refinement as witnessed from Figure1. These peaks are the impurity peaks which may are attributed to the un-reacted PbTiO3 phase.

   The absence of background noise revealed the complete phase formation, whereas, high peak intensity with sharpness witness crystallinity and narrow FWHM of these reflections is evident of higher average crystallite size. The average particle size of the material was calculated via Debye Scherrers equation and average size of particle was calculated to be 86 nm. Further, all the parameters related to the crystal structure and phase formation are documented in Table 1.

   Optical Bandgap Studies

   Room temperature Diffuse Reflectance UV-Vis spectroscopy (DRS) was exploited to throw light on the bandgap property of PbTi0.95Zr0.05O3 material. The recorded DRS spectra has been converted into KubelkaMunk functionand was plotted as [F(R)*hv]2 (n= 2 for the direct band gap transition) against E(eV)and the plots are displayed as in Figure 2, commonly known as Taucs plot. From this plot, band gap can be determined by extrapolating the linear portion of curve. The extrapolated line makes an intercept on energy axis and the magnitude of intercept is actually the band gap value. The energy band gap for the prepared sample was estimated to be

   3.1eV. The bandgap value is literally lower than parent PbTiO3 attributed to merging of an impurity band into the conduction band occurs which in turn shrinks the width of optical bnd gap. Further, it helps electrons to easy transfer from VB to CB. Besides this the interaction among the electrons and impurities would be the reason for reduction in width of electronic band gap [12-17].

   Yobs Ycalc

   Yobs-Ycalc Bragg_position

    

   3.1eV

    

   Intensity (a.u.)

    

   1.0

   0.8

   20 30 40 50 60 70 80

   (degree)

   Fig. 1. Rietveld Refinement of X-ray data of PbTi0.95Zr0.05O3 Perovskite.

   0.6

   [F(R)h]1/2

    

   0.4

   0.2

   0.0

   1 2 3 4 5 6

   E=h (eV)

   Table 1: Structural parameters obtained from XRD via Rietveld refinement
   S. No.	Parameters	values
   1	Space group	P4mm
   2	Crystal structure	Tetragonal
   3	Lattice parameters	a = b = 3.9980 and c= 4.10228 ()
   4	= =	90o
   5	Volume (3)	69.04
   6	Density(g/cm3)	11.34
   7	GoF	2.89
   8	2	2.77

    

   Fig. 2. Taucs plot for Optical band gap estimation of PbTi0.95Zr0.05O3 .

   Ac Conductiity Studies

   The Figure 3 shows the behavior of ac conductivity against logarithm of frequency at room temperature. It has been illustrated that ac conductivity is nearly independent in the lower frequency sites and referred to as dc conductivity whereas ac conductivity starts to increase with frequency at region of higher frequencies. A possible explanation for this behavior is that, at the beginning, when doping is applied to the material, charge carriers barely move and are confined in the material. As the frequency increases, after a certain value the charge carriers start penetrating the barriers and de-trapped with that the conductivity increases. Increase in the field speed

   up the movement of electrons, resulting in a rapid increase in conductivity. Thereafter any increase leads to the enhanced values of the ac conductivity by the sample [16-19].

   6E-05

   5E-05

   Conductivity (ac)

    

   4E-05

   3E-05

   2E-05

   1E-05

   0E+00

   1 2 3 4 5 6

   logf(Hz)

   Fig. 3. ac conductivity as a response to the applied frequency of PbTi0.95Zr0.05O3 Perovskite.

4. CONCLUSION

The polycrystalline sample of PbTi0.95Zr0.05O3 material was synthesized successfully by solid state reaction route. The tetragonal phase was witnessed from Rietveld refinement of XRD data of PZT. The particle size calculated using Scherers formula was found to be 86nm. The traces of PbTiO3 phase were witnesses which remains unfitted in the XRD diffractogram. The narrow FWHM and intensity of the reflections are witnessing the low particle size and the crystallinity of the sample. The optical bandgap from the Taucs plot was estimated to be 3.1eV which can be tailored to fit for opto-electronic devices particularly in high-temperature and power switching applications. The conductivity is considerably low thereby witness the insulating nature of the sample.

Futue Implications

As PbTi0.95Zr0.05O3 materials are better dielectric, piezoelectric, ferroelectric and exhibit wide band gap materials, it has potential applications in advanced technology. A pure crystal of PZT can be tailored from bandgap point of view to make it a strong candidate for RF signal processing, high-temperature and power switching applications and other optoelectronic device applications

ACKNOWLEDGMENT

The authors acknowledge SAGE University as an institute and Department of Physics, SAGE University for providing an opportunity to carry out this research project. Furthermore, the Faculty, labmates and are extended special thanks for cooperation..

REFERENCES

1. J. Frantti, S. Ivanov, S. Erikasson, H. Rundlöf, V. Lantto, J. Lappalainen,

   M. Kakihana, Phase transition of Pb(ZrxTi1x)O3 ceramics, Phys. Rev. B 66 (2002) 6410864123.

2. B. Noheda, D.E. Cox, G. Shirane, R. Guo, B. Jones, L.E. Cross, Stability of the monoclinic phase in the ferroelectric perovskite PbZr1xTixO3, Phys. Rev. B 63 (2001) 1410314112.
3. B. Noheda, D.E. Cox, G. Shirane, J.A. Gonzalo, L.E. Cross, S.-E. Park, A monoclinic ferroelectric phase in the Pb(Zr1xTix)O3 solid solution, Appl. Phys. Lett. 74 (1999) 20592061.
4. P. Ari-Gur, L. Benguigui, Direct determination of the coexistence region in the solid solutions Pb(Zr1xTix)O3, J. Phys. D Appl. Phys. 8 (1975) 18561862.
5. S.K. Mishra, D. Pandey, A.P. Singh, Effect of phase coexistence at LT morphotropic phase boundary on the properties of Pb(Zr1xTix)O3 ceramics, Appl. Phys. Lett. 69 (1996) 17071709.
6. V.A. Isupov, Comments on the paper X-ray study of the PZT solid solution near the morphotropic phase transition, Solid State Commun. 17 (1975) 1331 1333.
7. K. Kakegawa, J. Mohri, T. Takahashi, H. Yamamura, S. Shirasaki, A compositional fluctuation and properties of Pb(Zr, Ti)O, Solid State Commun. 24 (1977) 769772.
8. M.R. Soares, A.M.R. Senos, P.Q. Mantas, Phase coexistence region and dielectric properties of PZT ceramics, J. Euro. Ceram. Soc. 20 (2000) 321334.
9. Md. Ahamad Mohiddon, Abhishek Kumar, K.L. Yadav, Effect of Nd doping on structural dielectric and thermodynamic properties of PZT (65/35) ceramics, Physica B 395 (2007) 19.
10. V. A. Isupov, Reasons for discrepancies relating to the range of coexistence of phases in lead zirconate titanate solid solutions. Sov. Phys. -Sol. State, 22 (1) (1980) 98-101.
11. W. Wersing, W. Rossner, G. Eckstein, and G. Tomandl, the morphotropic phase boundary in PZT ceramics prepared by spray drying of salt solutions and by the mixed oxide method. Silic. Ind. 3-4 , (1985) 41-46.
12. T. Kala, Contribution to the study of tetragonal and rhombohedral phase coexistence in the PbZrO3 -PbTiO3 system. Phys. Stat. Sol. (a), 78 (1983) 277-282.
13. P. Ari-Gur and L. Benguigui, X-ray study of the PZT solid solution near the morphotropic phase transition. Sol. Stat. Comun., 15 1(974) 1077- 1079.
14. A. Barbulescu, E. Barbulescu, and D. Barb, Phase transitions in PZT solid solutions. Ferroelectrics, 47 (1983) 221-230.
15. V. A. Isupov, Properties of Pb(Ti,Zr)O3 piezoelectric ceramics and nature of their orientational dielectric polarization. Sov. Phys. -Sol. State, 10

    (4) (1968) 989-991.

16. L. Benguigui, On the properties of PZT solid solutions: a reply to a comment. Sol. Stat. Commun. 19 (1976) 979-981.
17. F. Vasiliu, P. G. Lucuta, and F. Constantinescu, Structure-sintering temperature relationship in PZT solid solutions at the morphotropic phase boundary. Phys. Stat. Sol. (a) 80 (1983) 637-642.
18. R. N. Perumal, S. Sadhasivam, V. Athikesavan,Structural, dielectric, AC conductivity, piezoelectric and impedance spectroscopy studies on PbZr0.52Ti0.48O3:RE3+(RE3+: La3+, Nd3+ and Dy3+) ceramics, Results in Physics, 15, (2019) 102729

[19]T. Garg, M. S. Malla, N. Kaurav, A. Yadav, The Co1xZnx Cr2O4 [x = 0.0, 0.1] chromite system: A study of structural and frequency dependent room temperature dielectric properties, Materials Today Proceedings, 89 (2023) 4-7